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| Home > Publications database > Zur Fischer-Tropsch-Synthese an multifunktionellen Cobalt/Zeolith-Katalysatoren |
| Home > Publications database > Zur Fischer-Tropsch-Synthese an multifunktionellen Cobalt/Zeolith-Katalysatoren |
| Book/Report | FZJ-2018-02512 |
1985
Kernforschungsanlage Jülich, Verlag
Jülich
Please use a persistent id in citations: http://hdl.handle.net/2128/18219
Report No.: Juel-2001
Abstract: The subject of this thesis has been to study the interaction of a metallic cobalt catalyst with zeolite supports and alkali as promoter in the CO hydrogenation reaction. For this purpose molecular sieves of the types of zeolite 4A, chabazite/erionite, ZSM-5, silicalite, mordenite and zeolite $\gamma$ as well as two silica carriers have been impregnated with aqueous cobalt-nitrate solution and reduced. The obtained catalysts were characterized by CO- and H$_{2}$-chemisorption, thermogravimetric analysis, X-Ray diffraction and electron microscopy. The catalytic activities of the Co/zeolite-catalysts were determined to be all about 6x10$^{-4}$converted CO per reduced Co per second. This value was half an order of magnitude less than those measured for the Co/silica-catalysts. Model calculations showed that a possible electrostatic field effect inside zeolite pores should be rather small. The hydrocarbon composition of the Fischer-Tropsch products followed the Schulz-Flory distribution. Chain growth, olefin-to-paraffin ratio and CO$_{2}$-selectivity grew in the order ZSM-5 < chabazite/erionite < mordenite < zeolite Y < zeolite 4A < silicalite and they correlated best with the basicity of the carriers increasing in the Same order. Experiments with Co/silica as well as with a Co-foil showed that alkali(Na, K) lowers the specific CO-hydrogenation activity and acts as an inhibitor for all the other hydrogenation reaction steps. The ratio between branched and linear hydrocarbons increased with increasing Si/Al-ratio of the zeolites in the order zeolite 4A <zeolite Y < chabazite/erionite < mordenite < ZSM-5. lt could be d emonstrated that folllowing reactions of the primary hydrocarbons on the supports can lead to a dramatic change in the selectivity pattern. Characterization by photoelectron spectroscopy of a Co-foil an which catalytic experiments were carried out made it possible to study the state of the unsupported Co-catalyst during CO-hydrogenation. The amount of deposited carbonaceous species grew with temperature, CO-partial pressure and reaction time. Alkali enhanced the deposition of carbonaceous species. Graphitic carbon (Cis electron binding energy : 284.4 eV) dominated on the unpromoted Co-foil, whereas an the promoted Co-foil mostly carbidic carbon (C1s-E$_{B}$ = 283,3 eV) and molecularly adsorbed CO (C1s-E$_{B}$ = 285,3-285,7 eV) were found. The carbidic phase is less catalytically active than the pure Co metal.
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